Method of inducing stress in glass containers and container made with a stressed zone



Oct. 20, 1970 FRANCEL ET AL 3,535,070

- METHOD OF INDUCING STRESS IN GLASS CONTAINERS AND CONTAINER MADE WITH A STRESSED ZONE Filed Aug. 5, 1966 FIG 5 ROBERT V. JAG-ODZI N SIG United States Patent fice 3,535,070 METHOD OF INDUCHNG STRESS IN GLASS CONTAINERS AND CONTAINER MADE WITH A STRESSED ZONE Josef France], Norman F. Gajewski, and Robert F. Jagodzinski, Toledo, Ohio, assignors to Owens-Illinois, Inc., a corporation of Ohio Filed Feb. 3, 1966, Ser. No. 527,395 Int. Cl. B65d 1/02; C03c 17/10 U.S. Cl. 215-32 20 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method of creating a prescribed pattern of stress in a glass container to facilitate its controlled opening at the stressed area having a greater predisposition to fracture. The invention involves a diffusion process of controllably weakening a glass surface in a prescribed manner by depositing on the surface of a defined pattern of a phosphoric acid solution containing soluble salts of certain metal cations, subjecting the deposit to an elevated temperature above the annealing point temperature to effect an ion exchange, and cooling the resultant deposit on the glass surface to create an inherent localized zone of stress adapted to controlled fracture by applying a bending moment.

The present invention relates to glass containers. More particularly, the present invention relates to those relatively small glass receptacles more commonly referred to and designated as ampuls, vials and like small vessels usually fabricated from tubing.

These small containers are advantageously used for packaging parenteral fluids, as Well as other substances, desirably hermetically maintained for later use, for example, by hypodermic injection. These small ampul-type containers are widely used in the medical, dental and related fields for hermetic storage of a variety of medicines, drugs, vitamins, etc. Veterinarians and those engaged in the field of animal husbandry also use these small ampultype containers for hermetically storing semen in small quantities as used in artificial insemination. These ampultype receptacles aer generally quite small for a number of reasons. Thus, the contents, desirably stored therein, frequently will become spoiled if opened to the atmosphere. Furthermore, the substances, are, in and of themselves, generally fairly highly concentrated such that small amounts are all that is necessary to accomplish a given end. Usually, several sizes of ampuls or vials ranging from 2-36 milliliters in volume size are generally sufficient to provide coverage for single dosages of the various medicines or liquids contained therein.

These ampul-type receptacles, and particularly those to which the invention are concerned, are those for which no separate closure element is employed. Rather, the packaging technique envisions an ampul or vial which is aseptic and, upon introduction of the substance therein, a generally restricted filling opening is heated to cause a running together of the glass surrounding the filling opening to close it. An ampul of the general type concerned herein is disclosed in FIG. 4 of the accompanying draw- Patented Oct. 20, 1970 ings; the ampul shown therein having an upper filling end 41 which has been fusion sealed.

The use of these ampul-type containers over the years has developed a need for the fabrication of these ampuls such that they can be relatively easily and controllably opened by the user preparatory to withdrawal of the contents and usually desirably without accompanying conamination and/ or spillage.

To provide the opening feature, it is generally known that the formation of a restricted neck portion, as at 42 in the drawings, will provide some measure of satisfying this need since the restricted neck portions will fracture easier than tubing of the size of the body porion 43 of the ampul 40. Additionally, the restricted neck portion is sometimes physically scored with a file or other abrasive element. It has also been fairly common to apply to an ampul outer surface a deposition of a second glass having an appreciably different coefficient of contraction as compared to the glass of which the ampul is formed. This has been found to create a stress differential generally along the margins of the applied second glass, whereupon a bending moment applied by the fingers of the user will provide a relatively clean break without the application of unreasonable bending moments of force as will lead to contamination, spillage and possible injury to the user.

With this general introduction, it may be stated that it is a principal object of the present invention to provide a method of treating a glass container whereupon it is given, along selected portions thereof, a predisposition to fracture upon the application of a bending moment, usually by the fingers and thumb of the user.

It is another object of the present invention to provide a method as described which is simpler, more reliable and more controllable than methods and tech niques known heretofore.

It is still another object of the present invention to provide a method as described which is eminently compatible with existing ampul, vial and like vessel manufacturing techniques.

It is another object of the present invention to provide a method as described which results in a change in the stress character of the wall, generally in a peripheral pattern, of the ampul, vial or the like.

It is still another object of the present invention to provide a method as described which, when practiced in accordance with preferred embodiments, provides the peripheral line having a predisposition to fracture; which line is relatively, substantially and practically invisible to the eye.

It is yet another object of the present invention to provide a method as described which employs treating agents which may be selected from commercially available substances and chemicals and which may be combined with a minimum of difiiculty.

It is still another object of the present invention to provide a method which employs treating materials which, when combined, are relatively stable and therefore not prone to change, deterioration or regression in strength or eflicacy.

It is still another object of the present invention to provide a method as described wherein accurate control of the amount of treating material applied is possible whereby the treating substance can be deposited in proportion to the wall thickness of the ampul involved as to thereby yield the appropriate predisposition to fracture.

It is yet another object of the present invention to provide a treatment which is essentially a chemical treatment, thereby obviating the necessity of physical modification as by scoring the ampul or other vessel.

The foregoing, as well as other objects of the present invention, will become apparent to those skilled in the art from the following detailed description taken in conjunction with the annexed sheet of drawings and the following recitation of examples; all of which are included purely for purposes of illustration of preferred manners and techniques for practicing the present invention in accordance with the requirements of the patent statutes.

In its mostbasic form, the present invention envisions a treatment of a glass container wherein there is deposited onto selected areas of the outer surface of the container a deposit of a phosphoric acid solution containing one or more salts of one or more metals selected from the group consisting of calcium, iron, lithium, magnesium, potassium, sodium and mixtures thereof and thereafter heating to effect a fusion of the deposit and a change in the stress character in the glass wall proximate thereto.

The phosphoric acid solution of various metal salts may be applied to the container in a variety of ways. Thus, it will be appreciated that a spray deposition may be accomplished using a masking screen having openings allowing the spray to be passed only onto selected portions as the container is rotated axially therebehind. Further, the deposition of solution containing the appropriate salts can be effected by a stenciling operation using a felt roller in contact with a pickup roller mounted to rotate with a portion thereof submergedly in an appropriate solution; More conventionally, a transfer wheel technique is utilized wherein the ampuls are rollably located in horizontal fashion 'with their end extremities supportedly in spaced parallel tracks. Intermediate the tracks, there is mounted a transfer wheel which, in its lower path, passes either into a bath of solution or against a pickup wheel which, in turn passes into a bath of solution whereupon the transfer wheel contacts the appropriate peripheral line location on which it is desired to deposit the solution. The ampuls, of course, may also be mounted in a battery of rotating chucks so controlled and moved that a transfer wheel is successively brought into contact with the outer surface to deposit the solution peripherally thereabout.

As indicated, any variety of techniques may be employed and the invention is not seen as residing in the method of deposition but rather in the make-up of the treating phosphoric acid solutions and, in combination therewith, the subsequent heat treatment thereof to effect the formation of a fused layer which, in turn, effects a change in the stress character of the underlying glass and proximate the margins of the line deposition.

Referring now more specifically to the drawings, there is disclosed in FIG. 1 an ampul 11 having a principal cylindrical body portion 12 and a tapered upper filling and dispensing end 13; the terminus 14 of which has been fused to hermetically seal the container at the time of filling. The ampul 11 is generaly formed of tubing originally having a diameter corresponding to the main body portion 12. In the restricted neck portion, intermediate the main body portions 12 and the end 14, there has been applied a spot deposition 15 of a solution in accordance with the present invention followed by a fusion heat cycle and as described more fully hereinafter. This spot deposition locates a Zone having a greater predisposition to fracture.

In FIG. 2, there is disclosed a similar ampul21 having the same component parts excepting that, in place of a spot deposition 15, there is located, in the restricted neck portion, a line deposition 25 which proceeds laterally about a considerable portion of the peripheral line describing the circumference at the restricted neck portion. This also imparts, after heat fusion, a zone having a predisposition to fracture.

In FIG. 3, vial having a rounded base end 31 and a heat sealed upper end 32 is provided with an elongate, fused deposition 35 on the outer surface as shown.

In FIG. 4, ampul bears in the restricted neck portion 42 a continuous annular band 45 composed of a heat fused line coating of a solution in accordance with the present invention. The combination of the neck-down area 42, the heat fused band 45 and the effect on the underlying glass cooperate in providing the optimum in predisposition to fracture along the band 45.

FIG. 5 is a schematic sectional view (greatly enlarged) taken on the line 55 of FIG. 3 of the elongate deposition 35. FIG. 5 serves to illustrate in schematic fashion that the deposit 35 is composed of a central raised portion (as shown) having marginal edges 36 and 36 where the stress differential in the wall W of the vial 30 is concentrated. Additionally, segment 38 of the wall underlying the deposition 35 represents an area in which the stress character of the glass has been changed as compared to that portion of the wall outside of the segment 38.

The formation of phosphoric acid solutions of metal salts is most conveniently accomplished using commercially available phosphoric acid solutions of fairly high concentration as will be more readily understood from the more detailed description to follow. To a proper amount thereof, there is added a salt, preferably soluble, of one of the metals enumerated hereinabove followed by stirring to achieve uniform distribution. A deposit of the solution is then simply applied to the ampul as a spot, segment of a line or a full annular line or band measuring preferably about 0.35 to 3.50 millimeters in width. Thereafter, the ampul bearing the applied solution is exposed to a temperature ranging from about 752 F. to about 1400 [400 C. to 760 C.] for from about 3 to 15 minutes. The make-up of the solution and the appropriate heat cycle cooperate in producing two effects. First, the heat fusion of the deposited solution components yields a glass-like layer securely attached to the substrate. Secondly, there is achieved a penetration of solution components, probably cations of the metals, into the glass. As indicated previously, these two phenomena cooperate to provide the desired predisposition to fracture along a line or band of preselected location. The fusion of the applied phosphoric acid solution of metal salts is conveniently accomplished during the annealing of the formed ampul. Preferably, the annealing is adjusted to include several minutes during which the temperature is controlled to just slightly exceed the annealing point of the glass used in fabricating the ampul.

The metal salt added to the phosphoric acid solution may be selected from available calcium, iron, lithium, magnesium, potassium and sodium salts including mixtures thereof. Of these salts, those that fall within Group I, namely, lithium, potassium and sodium, are preferred inasmuch as the data gathered in the exploration of these phenomena indicate that the desired ends are most eminently accomplished when salts of these metals are employed. The salts of those metals enumerated above which fall into Group II or Group III are also desirably utilized in the practice of the invention, particularly when combined with metal salts of lithium, potassium and sodium. Thus, it is believed eminently desirable to form treating solutions of phosphoric acid containing two salts, for example, a salt or salts of lithium, potassium or sodium in combination with a salt or salts of magnesium, calcium or iron.

The nitrates and carbonates of lithium, magnesium, potassium, calcium and sodium are preferred salts for utilization in the practice of the present invention since these metal salts, when applied as phosphoric acid solutions to the glass ampul, yield colorless bands after exposure to the elevated temperature for a time sufficient to effect fusion.

Thus, the glass-like fusion product of the phosphoric acid solution of those salts is practically indistinguishable from the base glass, at least as viewed by the naked eye. For comparative purposes, a band as just described is conveniently characterized as clear. Similarly, bands are also characterized as very clear, not so clear, fair, slightly frosty or definitely frosty.

Where absolute clarity (absence of color or cloudiness) is not essential, the metal salts for use in creating a zone having a predisposition to fracture may be phosphates, aluminates, silicates, titanates, borates, sulfites, manganites, fluorides, chlorides, sulfates, etc.

The relative breaking ease or a predisposition to fracture of ampuls can be assessed by simply breaking the ampul with the fingers and qualitatively judging it as being good, fair, poor or bad as compared to an untreated ampul. This ease of breaking is also determined quantitatively using the well-known Thwing-Albert Tensile Tester [Model 49RC] in which the ampul is appropriately mounted horizontally in a jig having a test span varying in accordance with the ampul size. A central, downwardly moving, breaking finger is then lowered against the ampul. The finger is controlled to move downwardly at a rate of 10 inches per minute. As indicated, the ampul is laid laterally between the supports at each end and the center breaking finger is allowed to move vertically down against the ampul until breakage occurs. An auxiliary strip chart recorder has a range of 100 pounds full scale for a 12 inch wide chart. The pin drive motor on the recorder travels full scale across the chart in 1.2 seconds. The scale records pounds of force necessary to achieve the breakage. A quantitative range of acceptable breakages for ten samples is listed in Table A below. As will be seen therein, the control ranges vary depending upon the size of the ampul. Ampuls may be 1 millimeter, 2, 5, 10, 20 or 36 millimeters in size. The Model 49RC Thwing-Albert Tensile Tester gives comparable results to those achieved by an Instron Tester,

TABLE A Ampul Control limits Upper control 99% limits for size Test for averages limit for range individual (ml) span (lbs. (lbs) ampuls (lbs) (inches) 1% -l2 10 5. 5-16 1% 9-12 10 5. 516 2% B ll 10 5-15 2% 1246 11 8-20 2% 13-17 12 0-21 In the examples and tables to follow, a break designation of good indicates that it falls within the limits in Column 3.

There will now be set forth in more specific detail a number of examples illustrating preparation of various phosphoric acid solutions of a number of metal salts falling within and representing preferred embodiments of the present invention. The tables in which the various examples are summarized also include a tabulation of the time/temperature cycle to which the solution-bearing ampul is subjected together with visual and breaking characteristics of the heat fused band.

There was first prepared six stock solutions of various volume percentages of phosphoric acid (H PO In preparing the stock solutions, there was utilized a commercially available phosphoric acid of 85% concentration as follows: 1

(a) 90 parts by volume of the 85% phosphoric acid were combined with 10 parts by volume of water to form 6 a solution having a concentration of 76.5% (H PO In the tables summarizing the various examples, this phosphoric acid solution will be identified as a 90/ 10 solution.

(b) parts by volume of the phosphoric acid were combined with 20 parts by volume of water making an 80/20 solution having an actual concentration of 68%. This is calculated as follows: of total parts, '80 thereof is 85 concentrated or, in other words, 80 .85=68 parts by volume of 100% phosphoric acid. Of the original 100, of course, 20 is water plus 12 (80-68) making a total of 32 parts of H 0.

(c) 70 parts by volume of the 85 concentrated phosphoric acid were combined with 30 parts by volume of water, yielding a 70/ 30 stock solution having an actual calculated phosphoric acid concentration of 59.5%.

(d) 60 parts by volume of the 85% concentrated phosphoric acid were combined with 40 parts by volume of water, yielding a 60/ 40 stock solution having an actual calculated phosphoric acid volume concentration of 51%.

(e) 50 parts by volume of the 85% concentrated phosphoric acid were combined with 50 parts by volume of water, yielding a 5 0/50 stock solution having an actual calculated phosphoric acid concentration of 42.5%.

(f) 30 parts by volume of the 85% concentrated phosphoric acid were combined with 70 parts by volume of water, yielding a 30/70 stock solution having an actual phosphoric acid concentration of 25.5%

In the examples to follow, it will be seen that the above stock solutions are used in combination with various proportions of various metal salts to form phosphoric acid solutions of metal salts in accordance with the present invention. In each case, 25 milliliter portions of the appropriate stock solution were selected and the indicated amounts of various salts were added together with other ingredients as noted. The application of the resulting salt-containing phosphoric acid solutions to the ampuls was accomplished using a transfer wheel whereby uniformity of application was achieved. Thereafter, the ampuls were subjected to an annealing cycle and thereafter a sampling of treated ampuls were inspected and their visual appearance and breaking strengths determined as described hereinbefore.

EXAMPLE 1 To 25 milliliters of a 60/40 phosphoric acid stock solution was added 10.8 grams of lithium nitrate, LiNO 2.2 grams of lithium carbonate, Li CO and 0.4 gram of Cab-O-Sil (a commercially marketed colloidal silica preparation). By transfer wheel, as described, a narrow line deposit of this solution was transferred to neck portions of a plurality of 36 ml. ampuls. Thereafter, the ampuls were subjected to an annealing or bake cycle of 1075 F. for 5 minutes. A check of the resulting ampuls in the manner described hereinabove revealed that the heat fused band was clear, the ampul could be broken easily by hand and the testing in the Thwing-Albert Tester fell within the quantitive limits enumerated in Table A.

Example 1 is summarized as to its important features in Table 1 below. Table 1 also includes a summary and tabulation of additional Examples 2ll2 similar to Example 1 except in the particulars noted. In Table 1, column 1 lists the particular example number. Column 2 identifiies the solution concentration of the phosphoric acid in terms of the ratio of 85 concentrated phosphoric to water. The actual percent of phosphoric acid can be determined from the description of the make-up of the stock solutions hereinbefore. Columns 3, 4, S and 6 identify various metal salts and the amounts of each added in the different examples. Column 7 lists the bake or annealing cycle as to temperature and time. Columns 8 and 9 contain a notation pertaining to the clarity of the band and the ease of breaklng, respecnvely, 1n accordylelds a band of frosty appearance and fair break charance w1th the code outlined 1n the footnotes (b) and (c). acter1st1cs.

TABLE 1 S01. Cone. LiNO LizCOa, Mg (N092, Cab-() Bnkc, FJ Clar- Exainplo 113F041L gm. gin. gm. Si1,g111. min. ity Break 40 .4 1,075 01 G .4 1, 075 5 o1- G .4 1, 075/5 cl G .4 1, 075/5 C4 F .4 1, 075 5 1 G .4 1, 005/ c1 F .4 1, 005 10 F .4 1,005 0 F1 F .4 1, 070 10 01 G 10 .4 1, 055/3 01 G 70 30 5 5 .4 1,055/8 01 G 70 30 4.15 .85 5 .4 1, 055 3 01- G 70/30 1.00 .34 8 .4 1,055/8 F G 70 30 0.04 1.30 2 .4 1,055 3 F G 30 70 1.00 .34 s .4 1, 055/8 Fr G 50 50 1.00 .34 3 .4 1,055 s 01 F 20 8.3 .5 1,075/5 (31 P 20 12.45 .5 1, 075 5 01- 1 50 12.45 .5 1,075 5 Fr 1 50 50 3.3 .5 1,075 5 01 P 80/20 4.15 .5 1,075 5 01+ Ext: 30 20 2.40 5 1,075 5 01 F a The concentration reported in this column is based on 85% II3PO1; so that; /40 means that 25 ml. Solution is 60 parts of 85% H PO and 40 parts of H20.

From the data in Table 1, specifically Example 17, In Table 2, further examples are summarized in which, it can be seen that a 30/ phosphoric acid solution, for purposes of comparison, varying amounts of several actually 25.5% H PO is yieldative of a band which is magnesium salts are included in the phosphoric acid visually frosted in appearance rather than clear as most 40 solutions and varying bake cycles are employed.

TAB LE 2 so]. cone. LiNOa, L12C03, Mg (N092, Mg 003, Bake F./ Example HaPOi gm. gm. gm. gm. min.

Clarity b Break Same meaning as in Table 1. b Same meaning as in Table 1. Same meaning as in Table l.

desired in the preferred practice of the invention. Ref- In Examples 70 and 79, the solutions also contained 0.9 erence to Example 10 reveals further that 20 grams gm. of Cab-O-Sil, while the other Examples summarized of lithium salts coupled with low H PO concentration in this Table2 contained 0.4 gm. Cab-O-Sil.

The results tabulated in Table 2 lllustrate the super1- of l1th1um and magnesium salts Were included in the only of lithlum salts and the acceptabillty of the magphosphoric acid solution.

TABLE3 sol. cone. LiNOs, 1112003, Mg (N092, Cab-O- Bake F./ Ex. HaPOl gm. gm. gm. sil,gm. Attagel min. Clarity Break .7 5.0 1,08 4% 01 G .7 0.3 mac/4% Fr F 2.8 4.8 080/4% 01 F 1.5 3.0 075/4 5 Cl P 1.0 1.0 075/4% 01 F .s 0.4 075/4% s1 F1 G 2.0 2.0 1, 075 4 1 B .8 0.0 1,075/4 01 G 9.0 1,075/4 01 G 10.0 1, 075/4 01 G 0.85 1,075 5 01 G 2.3 1,075/5 01 G 9.0 1,075/4 01 G 1.0 1.0 1,075/4 01 G 2.8 4.2 1, 075/4 01 G .8 7.2 1,075/4 G1 G 1.0 2.0 1,075 4. 01 G .7 .7 5.0 1,075 4 01 F 0.0 1,075/4 01 G /40 0 0 1, 075/4 F1 G Same meaning as in Table 1. Same meaning as in Table 1. 0 Same meaning as in Table 1.

Table 4 below contains a tabulation of further ex- 3 amples in which calcium salts are included in the phosphoric acid solution together with a lithium salt, specifically the nitrate and carbonate and in some cases both.

nesium salts, even alone, in particular amounts, but most preferably in combination with the lithium salts.

TABLE 4 S01. cone. LiNOs, LizCOs CaNOa, Cab-O- Atta- Bake Clar- Ex. 15131 0.; gm. gm. gm. Sil, gm. gel FJmin. ity b Break 0 60/40 1 0 9. 0 .4 F 60/40 4 15 85 5. 0 4 G 50/50 1 0 9. 0 4 G 60/40 7 5. (i 4 G 60/40 1 0 4. 0 9 G 80/20 1 0 4. 0 9 F 60/40 1 2 4. 8 9 G 60/40 6. 0 9 G 60/40 1 0 3. 0 9 G Same meaning as in Table 1. b Same meaning as in Table 1. 11 Same meaning as in Table 1.

50 Table contains a tabulation of other examples of the Table 3 above contains a tabulation of further eX- present invention representing employment of phosphoric amples of the present invention in which varying amounts acid solutions containing different ratios of lithium and magnesium salts and particularly magnesium phosphate.

TABLE 5 Mg- Mg- Cab- Atta- Sol. Cone. LiNOa, LiOOz, (N Om, (PO92, OSil, gel, Bake Clar- Ex. H3PO gm. gm. gin. gm gm. gm. F./min. ity b v oooom' oowewooooo g? p 0 Same meaning as in Table 1. b Same meaning as in Table 1. 0 Same meaning as in Table 1.

11 Table 6 below contains a tabulation of examples of miscellaneous formulations utilizing various metal salts in the phosphoric acid solution together with visual and breakage data on the resulting band.

12 With this in mind, it appears that the nitrates and carbonates of sodium, potassium and lithium are preferred metal salts in the preparation of phosphoric acid treating solutions since they yield a fusion band bearing TABLE 6 Cab- Atta- Sol. ratio LiNOa, O-Sil, gel, Run N0. 1131 040120 gm. gm. gm. Additional metal salt Clarity b IBreal-r 9 2. 2 6 gm. Al(NO3)s G 9 1. 3 gm. MgHPO4- 13 gm MgHPOr B 9 G 0 G 9 G 9 G 9 B 9 F 9 F 9 2 gm. lithium mauganit Purple F 9 2 gm. lithium titanate. White F .9 2gn1. Ll3PO4'H2O Cl G 8 5.4 gm. Mg(NOs)2, .3 gm. 01 G Z110. 8 5 5.4 gm. Mg(NO3)2, .3 gm. 01 G n .9 1.1 3 gm. MgHPO4 Fr F Same meaning as in Table 1.

Same meaning as in Table 1.

* Same meaning as in Table 1.

In the foregoing examples, the ampuls were formed of a glass having a compositional analysis within the ranges listed in Table 7 below.

Similar results were achieved with ampuls formed of soda-lime glasses and lead-type glasses. The glass in Table 7 has an annealing temperature of 575 C. (1064 F.).

EXAMPLE 113 (a) Four ampuls bearing fusion bands as produced in accordance with the procedure of Example 24 above were subjected to a stress analysis in the region of the applied band. The results showed the existence of compression stresses measuring from 880 to 1000 pounds per square inch. The average value for the four ampuls was 920 pounds per square inch.

(b) Four ampuls produced in accordance with Smith Pat. 2,517,604 were subjected to an identical stress analysis. The ampuls were fabricated of a glass identified as Glass A (at column 3) of the Smith patent while the band had a compositional make-up identified as Coating (a) (column 3) of the Smith patent. The results showed the existence of compression stresses measuring from 470 to 770 pounds per square inch. The average value for the four ampuls of this paragraph (b) was 630 pounds per square inch.

The stress analysis referred to in this Example 113 was performed with a polarimeter utilizing a birefringent quarter wave plate held in a Fisher optical cell and a Cargill immersion liquid having a refractive index of 1.560. The analysis technique is fully described in Chapter 9 of J. H. Partridges book Glass-to-Metal Seals published by the Society of Glass Technology of Sheffield, England (1949).

From the teachings of the foregoing examples, it will be seen that it is now possible, in accordance with this invention, to select (1) a combination of salts in proper amount thereof, (2) a phosphoric acid solution of appropriate concentration, and (3) a proper bake or fusion cycle as will yield an ampul bearing a band possessing the optimum in terms of visual clarity together with ease and uniformity of break, e.g., predisposition to fracture.

ampul of the optimum in properties. While we do not intend to be bound by any expression of a theory as to why these particular metal salts provide what is apparently the optimum in results, it is believed that these metals having a valence of +1 are more prone to undergo diffusion into the underlying layer of glass as the applied phosphoric acid solution is being fused by the baking cycle. A diffusion of sodium, potassium and lithium ions into the interstitial Si-OSi-O network, it is believed, would change the stress pattern as compared to the stress pattern in that portion of the glass 7 where diffusion has not taken place. It is further believed that the line between these two portions of different stress patterns represents a concentration of stresses creating thereby a predisposition to fracture. It is also believed that the band of fusion product which is, broadly speaking, a phosphate glass also contributes to the creation of a concentration of stresses in the underlying and contiguous areas.

The treating phosphoric acid solution may desirably include mixtures of several salts of differing cation moities. Thus, a Group I metal salt and a Group II metal salt are combined in a phosphoric acid solution as illustrated in the examples. The resulting fusion hands after application and baking are yieldative of a predisposition to fracture and are clear in most cases, The effect of the Group II metal salts, insofar as contributing breaking ease is concerned, is believed to stem from predominantly a fluxing action as opposed to a diffusion action.

Thus, from the tabulated data, it appears likely that, during the heating and fusion of the phosphoric acid solution (containing the magnesium and calcium salts) thereby forming the glass-like layer, a low melting flux is simultaneously formed by coaction of the Group II metal salts and the layer of glass just beneath the line of deposited solution. It is further suspected that the concentration of the phosphoric acid solution is a factor contributing to the formation of a low melting flux at the interface of the deposited solution and the underlying substrate. This resulting low melting flux, upon cooling, appears to form a glassy structure possessing a stress character or pattern different from that of the surrounding glass thereby resulting, in conjunction with the fused glassy band, in a line, particularly at the margins thereof, which lends to the ampul a predisposition to fracture.

Preferably, the phosphoric acid solution into which the metal salts are dissolved should constitute at least a 50/50 volume mixture of the phosphoric acid and water or, stated another way, the phosphoric acid concentration should measure at least about 40%. Lower concentrations lead to the formation of frosty bands lending little predisposition to fracture to the ampul. A preferred concentration for the phosphoric acid solution (in terms of desired breaking character and colorless appearance) is one ranging from about 59% (a 70/30 solution) to about 76.5% (a 90/ 10 solution).

The nitrates and carbonates are preferred salts in the practice of the present invention since examination of the ampuls resulting from the carrying out of the examples reveals that the amount of residue, as reflected in observation of cloudy and frosty bands, is a minimum when nitrates and carbonates are used. It is believed that this is perhaps due to the ready volatility of the CO and N moieties created by the decomposition of the nitrate and carbonate during the elevated temperature fusion cycle.

While it was at first thought that the added colloidal silica functioned primarily as a thickening agent aiding in the uniform application of the solution via the trans fer wheel, examinations of the tabulated data reveals that, with particular metal salt formulations, the colloidal silica is contributive to the achievement of a desired balance of clarity (absence of cloudiness or frostiness) and a controllable uniform break or fracture pattern.

The metal salts. are desirably held Within certain limits in terms of the weight amount per given volume of phosphoric acid solution. Thus, the data suggests that the total added metal salt in grams should not exceed the volume of phosphoric acid solution. Thus, for 100 ml. of phosphoric acid solution, the metal salt added should not desirably exceed in the aggregate 100 grams. This defines a weight/volume ratio of about 1.0 or less. Overall consistency in achievement of a clear, fracturable band is improved where the metal salt does not exceed 80 grams per 100 ml. of solution. Most preferably, the metal salts should, in aggregate, fall within the range of from about 20 to about 60 grams per 100 ml. of phosphoric acid solution, e.g., a weight/volume ratio of from 0.2. to 0.6. When the amount of metal salt is too high. the resulting band tends to lack clarity. Too little metal salt, particularly when coupled with low H PO concentration, yields a band lending little predisposition to fracture to the ampul bearing same.

While a phosphoric acid solution containing a single metal salt (preferably a nitrate or carbonate) will, upon baking, yield a clear band on an ampul and one lending a predisposition to fracture, the several variables of H PO concentrations, the temperature, the time and weight/volume ratio must be more closely controlled. Accordingly, it is preferred that the treating solution be composed of two or more metal salts differing as to anion and, even more desirably, differing in cation. Most preferably, one of the salts should be a lithium salt and ideally the lithium should predominate in weight amount.

A three salt combination in the phosphoric acid solution provides some advantages when considering mass production of ampuls bearing a clear fusion band in accordance with the present invention. Thus, with several phenomena involved, e.g., diffusion, fiuxing and the physical presence of the band itself, it is advantageous to provide an environment, in which all the physical and chemical changes possibly taking place, can in fact take place. This is most universally accomplished by the utilization of three soluble salts in forming the phosphoric acid treating solutions.

From the foregoing description, it can be seen that there has been provided a novel and controllable method for treating ampuls and like glass vessels with saltcontaining phosphoric acid solutions, followed by a temperate fusion thereof serving to yield an ampul bearing a band imparting a predisposition to fracture along a preselected zone.

It will be appreciated that the foregoing detailed de- 14 scription is primarily for the purpose of setting forth preferred and operative modes of practicing the invention. The invention should not however be considered limited thereto since obvious equivalents will be suggested to those skilled in the art from the foregoing, and all such obvious equivalents in materials and process steps are intended to be included within the scope of the present invention unless specifically excluded by the language of the appended claims.

We claim:

1. The method of creating a defined, pattern of stress in a glass container which comprises:

applying to a selected area of an alkali-metal containing surface of said glass container, a deposit of a phosphoric acid solution containing a salt of one of the metals selected from the group consisting of calcium, iron, lithium, magnesium, potassium, sodium, and mixtures thereof, and

subjecting the deposit to a time and temperature cycle sufiicient to cause a fusion thereof and effect a change in the stress character beneath and proximate the said deposit, the temperature being above the annealing point temperature of the base glass.

2. The method as claimed in claim 1 wherein the salt is dissolved in the aqueous solution of phosphoric acid.

3. The method as claimed in claim 2 wherein said phosphoric acid solution measures at least about 40% H PO by volume.

4. The method as claimed in claim 3 wherein said cycle ranges from about 3 to about 15 minutes in duration and from about 752 F. to about 1400 F. in temperature.

5. The method as claimed in claim 4 wherein said cycle includes at least several minutes at a temperature about 10 F. above the annealing point of the glass from which the container is formed.

6. The method as claimed in claim 4 wherein said solution contains a minor amount of colloidal silica.

7. The method as claimed in claim 4 wherein said salt is selected from the group consisting of carbonate and nitrate.

8. The method as claimed in claim 4 wherein metal has a valence of plus one (+1).

9. The method as claimed in claim 4 wherein metal has a valence of plus two (+2).

10. The method as claimed in claim 4 wherein metal has a valence of plus three (+3).

11. The method as claimed in claim 4 wherein solution includes at least one lithium salt.

12. The method as claimed in claim 11 wherein lithium salt is one of carbonate and nitrate.

13. The method as claimed in claim 12 wherein solution further includes a magnesium salt.

14. The method of inducing a defined pattern of stress in a glass container so that the container will have a predisposition to break along the margin of said pattern, which comprises:

applying to the alkali-metal containing surface of said container at ambient temperature a defined pattern of a deposition of a phosphoric acid aqueous solution-soluble-salts of the metals calcium, iron, lithium, magnesium, potassium, and sodium, and

subjecting said deposit to a temperature slightly above the annealing point of the glass for a period of about 3 to 15 minutes to replace, large ions of the base glass with smaller ions, and

cooling to substantially room temperature whereby the fused resultant of said solution of salts and phosphoric acid create in the substrate localized zones of stress corresponding to said pattern.

15. The method as claimed in claim 14 wherein said pattern is a line extending substantially peripherally about said container.

16. The method as claimed in claim 15 wherein said fused resultant is colorless.

said

said

said

said

said

said

17. The method as claimed in claim 4 wherein the said salt and phosphoric acid solution are present respectively in a weight volume ratio less than one (1.0).

18. The method as claimed in claim 17 wherein said ratio ranges from about 0.2 to about 0.6.

19. The method as claimed in claim 18 wherein said phosphoric acid solution measures at least about 60% H PO 20. A glass container having a localized area of stress differential providing predisposition to fracture along said area, said area being in part created by a fused coating carried by said substrate,

said coating comprising a heat matured phosphoric acid solution containing, initially, salts of the metals calcium, iron, lithium, magnesium, potassium and sodium and mixtures thereof.

References Cited 5 UNITED STATES PATENTS 10 ARTHUR D. KELLOGG, Primary Examiner US. Cl. XJR.

27 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.535.070 Dated October 20 1970 Invenc fls) JOSEF FRANCEL ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 46, "aer should be are-. Col. 2, line 13, "potion" should be portion-. Table 1, Ex. 4, "C

should be --Cl-; Table I, EX. 20, "20/20" should be 80/20-. Table 2, Ex. 34, "80/80" should be -80/20. Table 5, Ex. 91, "1975/4" should be --l075/4; Table 5, EX. 111, '2 .2" should be -2 .O--. Table 6, EX. 86, "60/50" should be 60/40. Col. 13, line ll, after "is" insertat-. Claim 14, line 60, after "aqueous" add -solution Signed and sealed this 24th day of April 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT lOTTSCI-IALK Attesting Officer Commissioner of Patents 

